DON'T ISOLATE the radials of your vertical from an earth connection.
This would be a disaster waiting to happen, both for safety and
lightning protection. Tying your feedline into your tower ground system
would be the best way to configure this. It should also be tied to
ground at your entrance panel and to the safety ground at your station
just like the grounds for all other antennas.
The amount of RF current you have going down this connection does effect
efficiency slightly. If you don't have a ground connection (and no
balun), that current would be conducted on the feedline as common mode
current and would contribute to feedline radiation and RF in the shack.
The amount of current that can exist on a ground connection (or the
feedline) is a function of how many radials you have, and whether or not
the ground system (or feedline) happens to be resonant. Bottom line is
that the effect on efficiency is NIL unless you only have a very few
elevated radials and the ground system happens to be resonant.
It's interesting to note that even with a good ground and a balun that
you can't prevent all feedline common mode currents. The field coupling
from the antenna will put currents back onto the feedline even if it is
perfectly decoupled at the antenna connection. This is the reason you
sometimes hear the suggestion of putting chokes a half wave away from
the antenna. However this is rarely required, except maybe when the
feedline happens to be a resonant length. Grounding is the same
situation, you can't prevent all ground currents even with elevated radials.
Jerry, K4SAV
Phil Clements wrote:
>
>
>>Subject: Floating Elevated Radials
>>
>>
>>
>>
>>>In transmitting systems elevated radials should never have a ground path.
>>>Grounding elevated radials reduces efficiency.
>>>
>>>
>>>If the house has a lot of noise and you receive on the transmitting
>>>
>>>
>>antenna >you might not want to directly ground the antenna ground system
>>to the >house. This is especially true with a small radial system.
>>
>>
>>
>>>73 Tom
>>>
>>>
> My elevated radials float, and are connected directly to the shield of the
> feed line. (7/8 inch Heliax.)
>
> When the other end of the Heliax is connected to the output of my amp, it
> is "grounded" to the "house" central grounding point because the chassis
> of the amp is strapped to it. Are you saying that the amp and transceiver
> should be isolated from "house" ground also? If so, just how much
> efficiency is gained?
>
> It has always been common practice to DC ground the radials of a ground
> plane antenna via the tower and its ground rod system, and by strapping
> the shield of the coax to the tower ground system at the base of the
> tower. Are you saying this method has less efficiency? If so how much
> less?
>
> (((73)))
> Phil Clements, K5PC
>
>
>>
>>
>
>
>
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